PHARM/PCS V5 · Procedure 31
Pharmacokinetics VI: Renal Excretion Data Following IV Administration
Separate total elimination from renal excretion after an IV dose, using urine collections alone.
What it computes
Following IV administration, determines Ke (total elimination) and Kr (renal excretion) from urine collection data. The procedure computes excretion rates, takes their logarithms, and regresses against midpoint collection times.
Inputs and outputs
You provide
- The IV dose
- For each urine collection: time, volume, and drug concentration
PHARM/PCS reports
- Ke, the total elimination rate constant
- Kr, the renal excretion rate constant
- Total amount of drug excreted
- A plot of log excretion rate against time
When to use it
When urine data are your primary source and you want to separate total elimination from the renal component, useful when plasma sampling is limited but collections are clean.
Reading the results
Plotting log excretion rate against the midpoint of each collection interval (not its end) is essential; the wrong time point biases the slope, and hence Ke. Wide or irregular intervals blur the rate estimate, so the tighter and more regular the collections, the more trustworthy Ke and Kr.
The arithmetic is done for you
From each collection's volume and concentration, the procedure works out the amount excreted, the excretion rate, the interval midpoint, and the logarithm before running the regression, so the midpoint rule is applied correctly every time. Results match the 1986 program to every printed digit.
This page describes the procedure. Calculations run inside the licensed PHARM/PCS V5 application. PHARM/PCS is a trademark of MCS Scientific LLC.